The present invention relates to methods and devices for the determination of the concentration of one or more alkali metal cations in aqueous liquids, such as serum, based upon detection of fluoresence.
Alkali metal cation concentrations are normally determined by ion selective electrodes, in which an ionophore membrane selective for the cation (e.g., valinomycin for potassium detection) coats an electrode equipped for potentiometric measurement. Various materials, including crown ether compounds, have been suggested for use in such devices.
The Ames Division of Miles Laboratories, Inc. has proposed dry chemistry tests for K.sup.+ involving a nonpolar membrane phase containing the ionophore valinomycin and either dye comigration into the membrane or dye deprotonation within the membrane. Clinical Chemistry, vol. 30, no. 6, p. 962, abstract 112 (1984). In either case the dye amount is determined by absorbance.
Fluorescence measurements of biological samples are sometimes made with devices employing fiber optics to convey light from the sample to a detector and/or to convey excitation light to the sample. Such devices are not used in the determination of alkali metal cations. Copending application U.S. Ser. No. 531,957 of Seitz, filed Sept. 14, 1983, describes the use of such a device in the determination of pH, employing dyes fluorescent in both protonated and deprotonated states. In Anal. Chem., vol. 54, pp. 821-823 (1982), L. Saari and W. R. Seitz describe a pH sensor based on immobilized fluoresceinamine.